How can I make my boobs firmer and less saggy after having my baby?

Exercise all muscles. Gravity ultimately wins. But doing upper body exercises including chest, pecs, abs and all other muscles groups can help. The older the boobs get, the more fat tissue and less glandular/muscles tissue is in them, so exercise chest muscles can help. When you r finished having babies, and have lots of $$, can consider plastics. Otherwise, get a good over-the-shoulder-boulder-holder.